An Image Guided Surgery System (IGS) provides a surgeon with spatial information. Typically, an IGS is used to indicate to the surgeon where the end or parts of a surgical tool is within or around the human body. For example, during brain surgery, one end of the tool might be in the surgeon's hand and the other end of the tool could be inside the patient, when it would not normally be visible. An IGS system finds the end of the tool that is outside the body, calculates (from tool geometry) where the other end of the tool is, and then registers the location of the tool with the prior images of the interior of the brain
U.S. Pat. No. 6,978,167 (Dekel) issued Dec. 20, 2005 to Claron Technology Inc discloses a method for detecting and tracking the pose of an object such as a surgical tool displaceable in a coordinate reference frame. A visible target pattern on a marker includes a series of contrast regions of dark and light for providing feature points at which the dark and light regions meet at a juncture of an optically detectable plurality of edges. The method and system determine the location of the feature points by first locating the edges using the change in contrast between contrast regions, and then determining junctures of multiple edges. A stereoscopic digital camera generates a pair of digital images of the target pattern and a marker template comprising a set of reference characteristics including a relationship between the feature points.
This patent discloses in detail a method for detecting the feature point at the junction of the contrasting regions, which method is particularly applicable herein so that the details of this patent are hereby incorporated by reference or may be referred to for further detail of the method.
U.S. Pat. No. 5,828,770 (Leis) issued Oct. 27, 1998 to Northern Digital Inc discloses a system for determining the spatial position and angular orientation of an object in real-time is provided having a sensor section and a plurality of markers which emit a detectable energy. The markers are activated in an initial marker-identification mode. With such system, because the markers have been each uniquely identified during the marker-identification mode, and the relative marker geometry is known, the markers are simultaneously activated, detected and tracked during a subsequent marker-tracking mode.
U.S. Pat. No. 5,923,417 (Leis) issued Jul. 13, 1999 to Northern Digital Inc discloses a similar system which includes a common energy detector for detecting both the energy emitted by an active target and the energy reflected by a passive target.
Existing state-of-the-art tracking technologies claims to have accuracy in the 2 mm range. These devices typically use infra-red or other non-visible optical tracking technology and suffer from a number of limitations including reduced capabilities with angulations of the tracked tool, difficulties in positioning a reference frame for tracking, inaccuracies from the positioning of the tracking reference as compared with the tracking field of view, and inaccuracies causes be contaminants (e.g., fingerprint on IR tracking sphere). These common problems lead to poor utility and inaccuracies in tracking tools during surgery.
Relying on multiple markers can increase the system error (larger inaccuracy), increase the footprint/size of the tracked device and lead to poor ergonomic design of tracked devices. The use of multiple generic markers in motion tracking applications (respiratory motion tracking) can place motion constraints on the tracking system that can lead to inaccuracies in motion tracking.
The standard markers that are available on the market today (IR spheres, X Points) do not have sufficient information associated with each marker to allow the use of a single marker (one IR sphere or X Point) to be used for tracking an object/device. This information only allows for a tracking system to measure the translational information of a single marker, since the system cannot determine rotational information from a sphere or symmetrical pattern. Tracking systems also have a problem distinguishing one marker from another, so the inclusion of multiple generic markers in a tracking systems field of view creates the problem of uniquely determining the identity of each marker and the object associated with it. If the objects are at rest the system could determine which object is associated with each marker, but if the objects are moving then the system will have a difficult time distinguishing one marker from another.
In order for these markers to be used in a tracking system multiple markers must be used and configured in a unique geometric pattern. Each unique pattern and associated markers are affixed to an object that needs to be tracked. This allows the tracking system to identify and track objects using multiple markers. Using multiple markers to construct a pattern has several disadvantages. The first disadvantage is that the size of the pattern will increase the footprint of the tracked object which could affect its usefulness. The second disadvantage is that since there is a large marker pattern associated with a tracked device, the ergonomic design of the device will be impacted. The final disadvantage is that the accuracy of detecting the position and orientation of a tracked object can be degraded. The accuracy of a tracked object is related to the accuracy in detecting the markers that are associated with it and the geometry of the pattern. Each marker has an associated error and when multiple markers are used this error can be compounded and magnified by the pattern's geometry.